Summary The US Airways Express (Trans States Airlines) Embraer 145LR aircraft (FlightLOF3504, registrationN829HK, serial number145281) departed Pittsburgh, Pennsylvania, on a flight to Ottawa/Macdonald Cartier International Airport, Ontario, with two flight crew, one flight attendant, and 28passengers on board. At 1720 eastern daylight time the aircraft landed on Runway25 at Ottawa and overran the runway, coming to rest approximately 300feet off the end of the runway in a grass field. There were no injuries. The aircraft sustained minor damage to the inboard left main landing gear tire. When the aircraft landed there were light rain showers. After the rain subsided, the passengers were deplaned and bussed to the terminal. Ce rapport est galement disponible en franais. Other Factual Information History of the Flight The flight from Pittsburgh was uneventful. Approaching Ottawa, the aircraft was radar vectored around storm cells for a localizer back course Runway25 approach to Ottawa/Macdonald-Cartier International Airport (MCIA). The aircraft was approximately 1.5miles north of the Ottawa non-directional beacon (NDB) at 2000feet above sea level (asl) and approximately 185knots indicated airspeed (KIAS) when air traffic control (ATC) issued the instruction for the final turn to intercept the localizer. This resulted in a shortened final approach, since the NDB is only 4.1nautical miles (nm) from the threshold of Runway25. The aircraft was then cleared to land. Although the airspeed was high, the inboard spoilers, which could be deployed in flight as speed brakes, were not extended. While attempting to capture the localizer, the aircraft drifted left and right of the localizer several times until on short final, less than one mile from the threshold. The flight crew had calculated the approach speeds as 133KIAS for a flap22 approach and 128KIAS for a flap45 approach. Because the aircraft was fast and on a high, shortened final approach, the flight crew prepared for a flap22 landing. The maximum speed permitted for the flap22 position is 200KIAS, and for the flap45 position, 145KIAS. At approximately three miles from the threshold and 180KIAS, the crew lowered the landing gear and selected flap22. The airspeed decreased to 150KIAS at one mile, and the aircraft crossed the runway threshold at 140KIAS, 75feet above airfield elevation (AAE). It then continued for 1675feet before reaching 50feet AAE. From 50 feet AAE to weight on wheels, the aircraft travelled approximately 2125feet, and the weight on wheels speed was 120KIAS. The landing, at approximately 1720 eastern daylight time,1 was smooth with no abnormalities. The aircraft was not equipped with thrust reversers; spoilers and wheel-brakes equipped with an anti-skid system were used to slow and stop the aircraft. On landing, all four spoilers deployed automatically and the brakes were applied, but the aircraft did not slow down as expected. About 11seconds after weight on wheels, the captain questioned the pilot flying (PF) about slowing the aircraft, and the PF advised that the brakes were not working. The captain took control of the aircraft and immediately applied the brakes, initially with no effect. Deciding that a go-around would not be possible, the captain pushed the control column forward to ensure that the nose of the aircraft was down and continued to apply the brakes. The brakes started to work effectively 16to 19seconds after weight on wheels, and the aircraft began to slow down, but it could not be stopped on the runway. After the landing, the aircraft and runway were inspected and showed no physical signs of skidding or hydroplaning. When hydroplaning occurs, the tires of the aircraft completely lose contact with the actual runway surface. They will continue to hydroplane until a reduction in speed permits the tires to regain contact with the runway surface. During total dynamic hydroplaning, the tire lifts off the runway and rides on a wedge of water, causing such a complete loss of tire friction that wheel spin-up will not occur. On wet runways, where there is not enough water to cause dynamic hydroplaning, viscous hydroplaning can occur. This term describes the normal slipperiness or lubricating action of water. Viscous hydroplaning does not reduce the friction to such a low level that wheel spin-up will not occur. On the other hand, reverted rubber hydroplaning can occur when a locked tire is skidded along a very slippery water- or slush-contaminated runway at any speed above about 20knots, at which point the friction-generated heat produces steam and begins to revert the rubber, on a portion of the tire, to its uncured state. Runway Data Runway 07/25 at Ottawa MCIA is 8000feet long, 200feet wide, with a smooth asphalt surface. It was raining at the time of the occurrence and the runway was wet, but there were no indications of excessive quantities of standing water. Flight Recorders The flight data recorder (FDR) and cockpit voice recorder (CVR) were sent to the TSB Engineering Branch for analysis. The FDR data indicated that the aircraft was configured for the landing with 22of flap. Weight on wheels occurred approximately 3800feet from the threshold of the runway, and the aircraft travelled a further 4500feet before coming to a complete stop. The vertical gdata indicated that the touchdown was very smooth. The hydraulic pressure for the braking system was plotted for the incident landing, and for the previous two landings, which had been conducted on dry runways. The brake pressure for all three landings started to rise at approximately six seconds after weight on wheels. The FDR records the brake pressures once per second. These records indicate that during the incident landing the brakes were active, although there were indications of low, fluctuating brake pressures, and the pressures did not rise above 500psi until approximately 16seconds after weight on wheels for the right brakes and 19seconds for the left brakes. This rise in brake pressure coincides with an airspeed of approximately 94 KIAS. The pressures continued to rise over the next nine seconds to approximately 2450psi for the right brakes and 900psi for the left brakes, at which point the aircraft left the runway. On the previous two landings the brakes were active and the pressures rose above 500psi within the first ten seconds and continued to climb to a maximum of approximately 1000psi over the next six seconds, at which point the pressures started to decrease. The occurrence aircraft was not equipped to record individual brake pedal positionsmore recently produced aircraft are so equippedso it was not possible to determine the amount of brake pedal deflection. The longitudinal acceleration trace for the incident landing showed an increase in deceleration from +0.08gto a constant deceleration of approximately 0.08guntil 15seconds after weight on wheels, when the brake pressures started to rise. The deceleration then rose steadily to 0.45gat which point the aircraft left the runway. On the previous landing the longitudinal deceleration increased to a maximum of approximately 0.20gin the first 16seconds after weight on wheels, and then started to decrease as the aircraft slowed. While attempting to download the information from the CVR, it was found that the recorded data had been erased. The CVR was taken to the manufacturer's facility in Seattle and the data was successfully recovered. The CVR showed that 31seconds before the end of the recording the CVR was powered down; the time recorded on the CVR from the aircraft UTC clock was 21:33:39. The CVR was then powered up again at 21:49:36, erased twice and then powered down six seconds after the second erase command was completed. Erasure of cockpit voice recorders is prohibited in Canada by Canadian Aviation Regulation (CAR)605.34 and in the United States by Federal Aviation Regulation (FAR)125.227. In accordance with Transportation Safety Board Regulations (subsection9(1)) when a reportable accident or incident takes place, the owner, operator, master, and any crew member shall preserve and protect any evidence relative to the reportable accident or incident. The deliberate erasure of a CVR in an attempt to destroy evidence, would be an offence punishable on summary conviction.2 Everyone convicted of such an offence is liable, pursuant to the Criminal Code of Canada, to a fine of not more than $2000or to imprisonment for six months or to both. Flight Crew The captain, who was the pilot non-flying, occupied the left seat. He held a valid airline transport pilot licence and had accumulated a total flying time of approximately 8000hours, with 4300hours on type. The first officer, who was the PF, occupied the right seat. He held a valid commercial pilot licence and had accumulated a total flying time of approximately 1860hours, with 900hours on type. His experience as PF on Embraer aircraft without thrust reversers was limited to approximately five flights. Weather The 2100 aviation routine weather report (METAR) for Ottawa MCIA was as follows: wind 220True at five knots, visibility 10miles in light rain showers, overcast cloud layer at 2100feet, altimeter setting of29.55. There had been recent thunderstorms. Performance Data (Weights and Charts) The landing weight of the aircraft was calculated using the initial fuel load from the pilot reports, estimates of the passenger and cargo weights, and the FDR recorded fuel flow for the duration of the flight. The landing weight calculation is summarized in AppendixA. The landing weight was estimated to be approximately 41000pounds. The reference approach speed (Vref) for an Embraer145LR at this weight is 132knots for flap22 and 127knots for flap45. Landing field length data charts were available from the EMB-145 Aircraft Flight Manual (AFM) with distances given as factored and unfactored. The unfactored landing distance, as defined by FAR25.125, is that distance between the aircraft when it is at 50feet AAE and when it has come to complete stop on the ground. Based on the weight of the aircraft, nominal values are provided for both dry and wet runways. The factored runway length includes a safety factor as described in FAR121.195. This builds a safety margin into the required runway length to allow for weather variations, landing technique, or a landing problem. The AFM safety factored landing distance for an aircraft landing weight of 41000pounds, with flap22, landing on a wet runway with winds 230at 5knots was 6500feet. The AFM unfactored landing distance for an aircraft in the same conditions is approximately 3900feet. Assuming a typical touchdown target of 1000 feet from the threshold, this gives an AFM-derived ground roll distance of approximately 2900feet. The actual ground roll distance of the aircraft as calculated from FDR data was approximately 4500feet, including the 300-foot overrun. The FDR-derived ground roll exceeded the AFM nominal value by 1600feet. The occurrence flight FDR data indicated that the distance between the aircraft when it was 50feet AAE to when it had come to a stop was 6625feet. Aircraft The Embraer 145LR is available with or without thrust reversers. At the time of the occurrence, the operator's Embraer fleet consisted of 22aircraft fitted with thrust reversers and 17aircraft without thrust reversers. Thrust reversers were not installed on the occurrence aircraft, and the aircraft was stopped using the wheel-brake system and the spoilers. The aircraft was equipped with four spoilers, two on each wing. The two inboard spoilers can be deployed in flight as speed brakes to help slow the aircraft. For this to occur the aircraft must be configured with the flaps at 0or 9, and the thrust lever angles must be below 50. With weight on wheels, all four spoilers deploy automatically when wheel speed exceeds 25knots and both engine thrust lever angles are below 30, or the N2 for both engines is below 56percent. The brakes are controlled through the brake control computer, which has two independent circuits, one for the outboard brakes and one for the inboard brakes. Hydraulic system1 and the essential DC bus1 supply the brake system to control the outboard brakes, and hydraulic system2 and the essential DC bus2 supply the brake system to control the inboard brakes. The main components of the brake system are the following: brake control unit (BCU), brake pedal transducers (BPT), inboard and outboard brake control valves (BCV), brake shut-off valves (BSV), pressure switches, check valves, hydraulic fuses, pressure transducers, and brake assemblies. The BCU contains all the circuitry to interface, control, monitor, and test the brake system components. This includes fault isolation and interfacing with the central maintenance computer and with the engine instrument and crew alerting system(EICAS). The BCU activates the brake system after it senses either weight on wheels and wheel speed of 50knots, or weight on wheels for three seconds. As soon as one of these requirements is met, hydraulic pressure will be available for braking. The amount of hydraulic pressure supplied for braking is proportional to brake pedal deflection through the BPT. If both pilots activate the brakes at the same time, the brake pressure is proportional to the pedals with the most deflection. Spring cartridges are installed in the BPT to provide a brake feeling to the flight crew; however, the spring cartridges do not provide brake feedback, they simply provide resistance at the brake pedals. Anti-skid protection controls the amount of hydraulic pressure applied by the pilots on the brakes. Anti-skid provides the maximum allowable effort for the runway surface in use, minimizing tire wear and optimizing braking distance. To perform this function, the BCU computes the wheel speed signal from the four speed transducers. When one of the signals decreases below the average of the remaining wheels, skidding is probably occurring and that brake pressure is relieved. After that, wheel speed returns to the average speed and normal braking operation is restored. For wheel speeds above 30knots, the anti-skid system activates the locked-wheel protection. If the slower wheel speed is less than or equal to 30percent of the faster wheel speed, the skid control circuitry sends a corrective signal to the associated brake valve. The brake valve commands a full brake pressure relief to the associated wheel, allowing the wheel speed recovery. The 30percent tolerance between the wheel speeds permits some differential braking for steering purposes. For wheel speeds below 30knots, the locked-wheel protection is deactivated, and the brake system actuates without the wheel-speed comparator. For wheel speeds below 10knots the anti-skid function is deactivated. Prior to the occurrence, there was a series of brake system component changes. This was done for company convenience; there was no prior indication of a brake problem on the occurrence aircraft. A full diagnostic check of the brake system was completed following the occurrence, and no anomalies were detected. As a precaution, the BCU was replaced and another full diagnostic was completed with no faults found. The occurrence BCU non-volatile memory (NVM) was later downloaded and four error codes were found. The BCU NVM does not record the time of the events. The manufacturer of this BCU indicated that the codes meant power had been interrupted. When error codes are generated, the messages BRK INBD INOP and/or BRK OUTBD INOP should be displayed on the EICAS. The error codes may also be generated during an APU start up, when a temporary loss of power in the BCU connectors could occur. However, this situation will not generate any EICAS messages because Embraer implemented delays on the EICAS during the APU start-up period. No EICAS messages were displayed during the incident landing roll. Other Incidents Two weeks after the occurrence flight, the same aircraft had a similar brake problem while landing in Montral. At the time, it was raining and the runway had a smooth, asphalt surface. The brake system was checked thoroughly and no faults were found in the system. The aircraft was released back into service and no additional occurrences have been reported.